Page 682 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

660 PART IV Specific Malignancies in the Small Animal Patient

Choroid plexus carcinomas may metastasize within the CNS by Diagnostic Imaging
a unique mechanism termed drop metastases in which cancer cells Computed tomography (CT) and MRI have revolutionized the
antemortem clinical diagnosis and management of brain tumors
are exfoliated into the subarachnoid space or ventricular system
VetBooks.ir with eventual distant implantation of tumor foci. Finally, SBTs in veterinary medicine. 40–43 MRI is the preferred modality for
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that spread hematogenously often result in multiple metastases
the evaluation of intracranial disease. Information obtained from
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within the brain (see Fig. 31.1). imaging such as tumor number, origin within the neuraxis (extra-
axial, intraaxia, or intraventricular) and intrinsic signal appear-
Diagnosis of Intracranial Tumors ances, often collectively provides characteristic patterns that allow
for the presumptive diagnosis of the most frequently encountered
The index of suspicion for a brain tumor as a potential etiology PBTs and SBTs. In one investigation, the accuracy of predicting
for the observed clinical signs is based upon signalment, his- the type of PBT based on MR images of was 70%. 40
tory, and neurologic examination findings. In addition to brain Meningiomas (Fig. 31.2 and see Figs. 31.1A, C) are the most
tumors, differential diagnoses in dogs and cats with focal intra- common extraaxial origin tumors in dogs and cats. 3,33–34 Menin-
cranial disease include anomalies/malformations, infectious or giomas typically have a broad-based skull attachment, have dis-
immune-mediated meningoencephalitis, traumatic brain injury, tinct tumor margins, and demonstrate marked and often uniform
and stroke. For those animals with a multifocal or diffuse local- contrast enhancement (see Fig. 31.2). Some meningiomas will also
ization, metabolic disorders, neurodegenerative diseases, and display intratumoral fluid (see Fig. 31.2A), large cystic regions,
meningoencephalitides should be considered. A logical and pri- intratumoral mineralization, calvarial hyperostosis, or a dural tail
oritized diagnostic approach to patients with suspected brain sign (see Fig. 31.2). Calvarial hyperostosis can result from tumor-
tumors is indicated. induced reactive osseous changes or tumor invasion into bone. 3,44
The dural tail sign is a contrast-enhancing, linear thickening of the
Minimum Database dura mater extending from an adjacent extraaxial mass and is not
Laboratory evaluation of health status (complete blood count, specific for meningioma (see Fig. 31.2) or for neoplastic diseases
serum biochemistry, urinalysis) is important, as anesthesia is in general. 45,46 Peritumoral edema is observed in more than 90%
recommended for diagnosis of structural brain disease. The at- of canine meningiomas (see Fig. 31.1A). 20,40,41 In canine stud-
risk population of middle-aged to older animals with brain ies, reported sensitivities of MRI to correctly identify intracranial
tumors may also have significant concurrent disease that affects meningiomas range between 60% and 100%, 20,40,47 but specific
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management. 2,38 grades and subtypes cannot be distinguished. The MRI sensi-
Thoracic radiographs and an abdominal ultrasound (AUS) tivity for meningiomas has been estimated to be 96% in cats.
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should be considered in an attempt to identify concurrent unre- The imaging features of HS, granular cell tumors, and hemangio-
lated neoplasia or other significant comorbidities. Studies have blastomas share similarities with those of meningiomas (see Fig.
reported contemporaneous and unrelated neoplasms in 3% to 31.2). 41,42,49
23% of dogs with PBTs, the majority of which involved the As gliomas originate within and may infiltrate and displace the
thoracic or abdominal cavities. 2,39 Recent studies have shown neuropil, they often appear poorly marginated and may or may
that although abnormalities are frequently identified on tho- not demonstrate contrast enhancement. 40–42,50 Among contrast-
racic radiographs and AUS in dogs with PBT, the results of enhancing gliomas, the patterns and degree of enhancement seen
these procedures uncommonly (1.3%) negatively affected the can be highly variable. A “ring enhancing” pattern, in which a
decision to pursue advanced neurodiagnostics indicated for the circular ring of contrast enhancement surrounds nonenhanc-
neurologic condition of the patient, and significantly altered ing abnormal tissue, is often associated with gliomas (Fig. 31.3).
therapeutic recommendations for the brain tumor in 8.0% of However, ring enhancement is a nonspecific finding that has been
cases. 38,39 For clinically stable patients with a suspected brain associated with neoplastic, vascular, and inflammatory brain dis-
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tumor and unremarkable general physical examination, the eases. Currently, using conventional CT or MRI sequences, it is
authors do not routinely perform screening radiographs or AUS not possible to reliably differentiate types of gliomas (astrocyto-
before MRI, but do recommend these procedures before brain mas from oligodendrogliomas) or accurately predict the grade of
tumor treatment. gliomas. 40,50 The considerable overlap that exists in the imaging

A B C D
• Fig. 31.2 Postcontrast magnetic resonance image features of intracranial meningioma and its imaging mim-
ics. (A) Feline meningioma, with intratumoral fluid (arrow). (B) Canine histiocytic sarcoma. (C) Canine granular
cell tumor. (D) Canine parasagittal meningioma. Each of the canine tumors features a dural tail sign.